The present invention relates to a support and locking device for nozzles of a high-pressure stage in gas turbines.
As is known, gas turbines are machines which consist of a compressor and of a turbine with one or more stages, wherein these components are connected to one another by a rotary shaft, and wherein a combustion chamber is provided between the compressor and the turbine.
In order to pressurise the compressor, it is supplied with air obtained from the outer environment.
The compressed air passes through a series of pre-mixing chambers, which end in a converging portion, otherwise known as the shroud, into each of which an injector supplies fuel which is mixed with the air, in order to form an air-fuel mixture to be burnt.
In order to improve the combustion characteristics, there is generally provided an element which intercepts the flow of air obtained from the compressor, and has a complex shape, consisting of two series of blades, oriented in opposite directions, all of which is designed to produce turbulence in the air-fuel mixture.
There is admitted into the combustion chamber the fuel, which is ignited by means of corresponding spark plugs, in order to produce the combustion, which is designed to give rise to an increase in the temperature and pressure, and thus to enthalpy of the gas.
Simultaneously, the compressor supplies compressed air, which is passed both through the burners, and through the liners of the combustion chamber, such that the said compressed air is available to assist the combustion.
Subsequently, via corresponding ducts, the high-temperature, high-pressure gas reaches the various stages of the turbine, which transforms the enthalpy of the gas into mechanical energy which is available to a user.
In two-stage turbines, the gas is processed in the first stage of the turbine, in temperature and pressure conditions which are quite high, and undergoes initial expansion there; whereas in the second stage of the turbine, the gas undergoes second expansion, in temperature and pressure conditions which are lower than in the previous cases.
It is also known that in order to obtain the best performance from a specific gas turbine, the temperature of the gas needs to be as high as possible; however, the maximum temperature values which can be obtained when using the turbine are limited by the resistance of the materials used.
In order to make apparent the technical problems which are solved by the present invention, a brief description is provided hereinafter of a stator of a high-pressure stage of a gas turbine according to the known art.
Downstream from the combustion chamber, the turbine has a high-pressure stator and rotor, wherein the stator is used to supply the flow of burnt gases in suitable conditions to the intake of the rotor, and, in particular, to direct it in an appropriate manner into the apertures of the rotor blades, and prevent the flow from meeting directly the dorsal or convex surface and the ventral or concave surface of the blades.
The stator consists of a series of stator vanes, between each pair of which a corresponding nozzle is provided.
The group of stator vanes is in the shape of a ring, and is connected externally to the turbine housing, and internally to a corresponding support.
In this respect, it should be noted that a first technical problem of the stators, in particular in the case of high-pressure stages, is caused by the fact that the stator is subjected to high pressure loads, owing to the reduction of pressure of the fluid, which expands in the stator apertures.
In addition, the stator is subjected to high temperature levels, owing to the flow of hot gases obtained from the combustion chamber and, to the flows of cold air which are introduced into the turbine, in order to cool the parts which are subjected to the greatest stress from a thermal point of view.
Specifically because of these high temperatures, the stator vanes which are used in the high-pressure stage of turbines must be cooled, and, for this purpose, they have a surface which is suitably provided with holes for ducts, which permit circulation of air inside the stator vane itself.
Another problem which is particularly well known in the art is that of guaranteeing optimum support and locking of the stator vanes, in particular in the high-pressure stage.
In addition, conventional stators have support and locking systems which do not permit easy dismantling, when this is necessary in order to carry out operations of maintenance or replacement of one or more stator vanes which are worn or damaged.
Another problem consists in the fact that the stators are subject to the vibrations transmitted by the stator vanes during functioning of the machine.
However, the stator vanes must have small dimensions, because the high-pressure gases have a very high density; this means that the cross-sections of passage of the first stages must be considerably smaller than the cross-sections of passage of the subsequent stages, when the gas has undergone initial expansion.
The object of the present invention is thus to provide a support and locking device for nozzles of a high-pressure stage in gas turbines, which is particularly reliable.
A further object of the invention is to provide a device which has a simple and compact structure.
A further object of the invention is to provide a device which has a low cost, and consists of a reduced number of component parts.
Yet another object of the invention is to provide a support and locking device for nozzles of a high-pressure stage in gas turbines, which permits easy fitting and dismantling of the stator vanes as required, in order to carry out maintenance and optionally replacement of the latter.
A further object of the invention is to provide a device which permits optimum distance to the vibrations which affect the stator vanes, and to prevent these vibrations from being transferred to the other elements of the motor.
A further object of the invention is to provide a device which is safe, simple and economical.
These objects and others are achieved by a support and locking device for nozzles of a high-pressure stage in gas turbines, comprising a plurality of groups of stator vanes, which are associated with a plurality of outer sealing plates for connection of these groups to the outer liner of the combustion chamber, and are associated with a plurality of inner sealing plates, for connection to the inner liner of the combustion chamber, characterised in that each of the said groups of stator vanes is locked at an inner ring, wherein the said ring has a first series of outer holes to reinforce this locking, and a second series, of inner, through holes, which are provided in an inner extension of the said ring, and are used to secure the ring itself to the structure of the gas turbine.
According to a preferred embodiment of the present invention, each of the groups of stator vanes has outer slots for engagement with the outer sealing plates, and inner slots for engagement with the inner sealing plates.
In addition, each of the groups of stator vanes is connected via the outer slots to the outer sealing plates, by means of a first group of pins, and via the inner slots to the inner sealing plates, by means of a second group of pins.
According to another preferred embodiment of the present invention, a peripheral portion of the ring has a circumferential groove, which communicates with the through holes, which in turn are aligned with corresponding blind holes.
According to a further preferred embodiment of the present invention, the groups of stator vanes have on their interior plates which are provided with holes, wherein these plates are inserted inside the circumferential groove, such that the holes communicate with through holes in order to reinforce the locking of the groups of stator vanes onto the ring, by means of pins.
According to a another preferred embodiment of the present invention, each of the groups of stator vanes has projections which abut the body of the gas turbine.
According to another preferred embodiment of the present invention, the ring has a duct which communicates between the exterior of the combustion chamber, and the downstream portion of the groups of stator vanes, which opens onto a front portion of the ring, and has a first portion, and a second portion, which has a diameter smaller than the first portion, and wherein the first and second portions are connected to one another by a further, frusto-conical portion.
In addition, the duct opens in the rear portion of the ring, facing the said plate-type element, into a final, frusto-conical portion.
Further characteristics of the invention are defined in the claims which are attached to the present patent application.